1. Technical Field
The invention is related to a method of quantitatively measuring the amount of capacitive coupling of RF power in an inductively coupled plasma, and in particular to measuring the amount of capacitive coupling of RF power to a semiconductor wafer in an inductively coupled RF plasma reactor.
2. Background Art
In various plasma processes carried out in semiconductor wafer processing, precise control of ion bombardment energy at the wafer surface is crucial to process performance. For example, etching a polysilicon layer formed over a thin oxide layer (e.g., the gate oxide layer) requires high polysilicon selectivity and etch anisotropy during the entire process. This in turn requires a narrow distribution of plasma ion energy about an optimum ion energy. A problem is that capacitive coupling in an otherwise inductively coupled plasma broadens the plasma ion energy distribution, thereby reducing process performance. Therefore it would be helpful to measure the amount of capacitive coupling and the amount of inductive coupling in an inductively coupled plasma. However, there is no known method for quantitatively measuring the amount of capacitive coupling of RF power in an inductively coupled plasma.
It is therefore a principal object of the invention to provide a method of quantitatively measuring the amount of capacitive coupling in an inductively coupled RF plasma.